The invention relates a control device for the adjustment of the injection timing and/or the delivery rate of a fuel injection pump for IC engines in which the control signals from a microprocessor are transmitted by way of an electrical stepper motor via motion transmitting members with an intermediate spring force storage means to a control rod of the pump.
A control device with these features has been proposed in the European Pat. No. 00 69 111 B1 whose spring storage means serves the following purpose: When the microprocessor brings about a setting step which coincides with a pumping event in the injection pump the control rod is then temporarily locked so that it cannot be set, but if however the storage means temporarily accepts one or more steps of the electrical servo motor as a sort of buffer it may then pass on such temporarily stored steps when the control rod is no longer locked so that all the setting steps may be effected, i.e. converted into a respective resetting the position of the control rod. Furthermore in the form of the invention shown in FIG. 2 there is a security device in the form of a return spring connected with a hydraulic controlling device with which the control rod may, when needed, be moved out of any desired set position quickly into the zero delivery position. The prior art control device is however excessively elaborate in every respect both as regards the amount of components and also as regards the amount of space and not only with respect to the last-mentioned security device but also with respect to the overall mechanical setting step transmitting system.
In control devices of the initially mentioned type reference and check signals are required for coping with the operating commands to which the stepper motor has to respond for a respective setting of the control rod. The reference signals which are supplied to the microprocessor as command signals are as a rule supplied by devices such as tachometer generators, which are located on the crank shaft or a cam shaft of the IC engine. As a rule there is no provision for feedback indicating whether the commands from the microprocessor have been correctly performed by the stepper motor, because when there is a spring force storage means included in the transmitting means connecting the stepper motor with the control rod it is fair to assume that the desired setting will be effected, possibly with a slight lag in time. However, this assumption will only apply for the case in which the control rod is generally free to move, i.e. not impeded. In cases in which for one reason or another the control rod is locked for a prolonged time (and not just for a short time) they are not able to be detected by the control device and are thus not taken into account. This is found to be a disadvantage as well in the control device of the said European Pat. No. 00 69 111 B1.
Furthermore the German unexamined specification No. 2,417,771 describes a control device of the initially specified type, in which a stepper motor, motion transmitting members connecting it with the control rod, a return spring and a tachometer generator are present arranged within a closed housing flange-mounted on the injection pump. The same parts are furthermore exactly customized to suit the type of injection pump with which they are utilized. The rotor of the stepper motor used in the system in such that its drive shaft may practically only perform a relatively small rotational movement of 90.degree. at the most, because of the motion transmitting members used, in order to move the control rod along its full stroke. This means that only a relatively coarse setting is possible. The encapsulation of the components in the housing is a shortcoming inasfar as the parts therein may only be taken out of it, for example for a repair, after complex and extensive dismounting operations. They may then be replaced by intact parts. Since the parts of the assembly are customized to suit one specific injection pump it is practically impossible to use them in any other injection pumps and types thereof.